The present invention is related to pressurized cleaning systems, particularly one which uses a vacuum line for the pickup of the cleaning liquid and dislodged contaminants from a dirty tank or other dirty surface, removes the dislodged contaminants from the cleaning liquid and recycles the cleaning liquid for spraying against the dirty surface.
Industrial tanks are often cleaned after the tank is empty. To do so the interior of the tank is usually sprayed with cleaning liquids to dislodge the contaminants, both liquid and solid, from the tank surfaces. The pumps used typically operate at pressures ranging from about 1000 to 10,000 psi. Because the impact of the spray is diffused if there is a liquid layer within the tank, it is desirable to keep the amount of cleaning liquid (as well as dislodged contaminants) which collects at the bottom of the tank to a minimum.
Oil tankers pose special problems for tank cleaning apparatus. Oil is pumped out of the ground commonly contains rocks, sand and gravel. In addition to this naturally present foreign matter, a great number of rags find their way into the oil holding compartments of oil tankers. The presence of contaminants of types which both float and sink create additional problems during cleaning operations when the cleaning liquid is recycled.
A tank cleaning system has been used wherein a cleaning liquid is sprayed into the tank and simultaneously sucked out of the tank. This cleaning system is illustrated in U.S. Pat. No. 4,466,154 at FIGS. 1 and 2. The cleaning liquid is stored in a pressure vessel and incompletely fills the vessel so that a space is left above the free surface of the liquid. A pressure pump draws the liquid from the lower regions of the vessel and forces the liquid through a pressure line to a gas fired heat exchanger. The cleaning liquid is heated as it passes through the heat exchanger and then passes through a line where the high pressure, high temperature liquid is used to clean inside of the tank.
Simultaneously with the spraying of the cleaning liquid in the tank, a vacuum line, with this known method, draws the sprayed cleaning liquid and dislodged contaminants from the bottom of the tank. The vacuum line terminates at the pressure vessel where the cleaning liquid and contaminants are discharged into the cleaning liquid therein. A partial vacuum is created within the space above the free surface of the liquid within the pressure vessel by a vacuum pump. Cleaning liquid and contaminants withdrawn from the tank never pass through the vacuum pump.
Although the available systems will allow tanks to be cleaned using recycled cleaning liquid, they lack an efficient method for handling solid contaminants.